Catalytic process for preparing a high molecular weight cis-1,4-polyisoprene



United States Patent 3,479,331 CATALYTIC PROCESS FOR PREPARING A HIGHMOLECULAR WEIGHT CIS-1,4-POLYISOPRENE Kan Mori, Taro Suminoe, TamotuYamazaki, Tunezo Ishikawa, and Akira Kogure, Yokkaichi-shi, Japan,assignors to Japan Synthetic Rubber Co., Ltd., Tokyo, Japan, acorporation of Japan No Drawing. Filed Dec. 18, 1967, Ser. No. 691,161Claims priority, application Japan, Dec. 26, 1966, 41/ 84,450 Int. Cl.C08d 1/14 US. Cl. 26094.3 4 Claims ABSTRACT OF THE DISCLOSURE Highmolecular weight cis-l, 4-polyisoprene is produced by contactingisoprene in a hydrocarbon solvent with a catalyst obtained by admixing(A) a titanium tetrahalide, (B) a complex of boron trifluoride with aphenol, and (C) a trialkylaluminiurn. Preferred catalyst is prepared byadding (A), optionally in the presence of isoprene, to a reactionmixture of (B) with (C), the proportions of the three components beingsuch that TizAl is 1:05 to 1:10, and Al:B is 3:1 to 15:1.

This invention relates to a process for the preparation of polyisoprene.More particularly, the invention relates to a process for thepreparation of a cis-1,4-polyisoprene having an extremely high molecularweight and a Widely varying gel content, with the use of a novelcatalyst which has a high polymerizing activity.

It is well known that the molecular weight of natural rubber orcis-1,4-polyisoprene having substantially the same molecular structureas natural rubber (hereinafter referred to simply as polyisoprene) isreduced when milled on roll or in Banbury mixer. The polyisoprene as rawrubber for practical use must have the molecular weight approximately tothat of masticated natural rubber (which is 4-5 when expressed by anintrinsic viscosity [1;]). From an economical standpoint, preparation ofoil-extended polyisoprene is also desirable. In this case, however, thebase polymer must be of a sufiicient high molecular weight to secure theeconomical advantage. Therefore, in the preparation of polyisoprene,high molecular weight of the product polymer is a critical requirement.

The gel content of the product polymer is another important factor. Itis a common knowledge, in general, that the gel content of the elastomeraffects to a great degree the processability of the elastomer and alsothe properties of the vulcanized product. This also applies to thepolyisoprene. Therefore, if the gel content of the polyisoprene can befreely controlled from a very minimum to a substantial amount, a widevariety of the vulcanized products suitable for different usages may beconveniently obtained.

The preparation of a high molecular weight polyisoprene, however, isvery difficult by using titanium tetrachloride-trialkyl-aluminiu mcatalyst which is known for its excellent catalytic activity forpolyisoprene formation, without lowering the polymerizing activity ofthe catalyst. Also with the use of this type of catalyst, gel content ofthe product is invariably high (e.g., E. Schoenberg et al., Advances inChemistry Series 52, p. 6, American Chemical Society, Washington, DC,1966).

It has now been found that a novel catalyst, which is highly active inthe polymerization of isoprene and is capable of producing a highmolecular weight cis-l,4- polyisoprene, can be obtained with acombination of a titanium tetrahalide, a complex of boron trifluoridewith a phenol, and a trialkylaluminium. It has also been found ice thatsome of the novel catalysts disclosed in this specification can producesubstantially gel-free polymers.

Accordingly, the present invention provides a process for thepreparation of a high molecular weight cis-1,4- polyisoprene, whichcomprises contacting isoprene in a hydrocarbon solvent with a catalystwhich is obtained by admixing (A) a titanium tetrahalide, (B) a complexof boron trifluoride with a phenol and (C) a trialkylaluminium.

As the catalyst component (A), any of tetrachloride, tetrabromide, andtetraiodide of titanium can be used. However, titanium tetrachloride isthe most preferred.

The boron trifiuoride-phenol complex, which is the catalyst component(B), can be prepared by passing boron trifluoride gas through thephenol. As for the phenol, rnononucleus monohydric phenols such asphenol and metacresol are preferred.

The catalyst component (C) is selected from the trialkylaluminiumsrepresented by a general formula AlRR'R (in which R, R, and R" eachstands for an alkyl group, which may be the same or different. The typeof the alkyl group is not critical, which may be straight or branchedchain. Alkyl groups having 1-20 carbon atoms are preferred, and thosehaving 1-8 carbon atoms are the most preferred. Preferredtrialkylaluminiums include: trimethylaluminium, triethylaluminium,tripropylaluminium, tri-n-butylaluminium triisobutylaluminium,trihexylaluminium, and trioctylaluminium.

The catalyst of this invention can be prepared by mixing the above threecomponents, (A), (B) and (C) under an inert gas atmosphere, preferablyin a hydrocarbon solvent. It is preferred that the components (B) and(C) are first mixed and then the component (A) is added thereto. Thecatalyst may also be prepared by mixing the three components in thepresence of a part or whole of the isoprene to be polymerized. In orderto obtain both a high molecular weight polymer and an extremely highyield, it is recommended to mix the three catalyst components in theabsence of isoprene, or in the presence of at a maximum of 10 molartimes the component (A) of the isoprene, and thereafter to age themixture. The aging time differs depending on the aging temperature.Usually shorter aging time is sufficient under higher temperature. Forexample, at 10 C. approximately an hours aging is preferred, but at 20C. or higher, 30 minutes aging is sufficient.

The ratio between components (B) and (C) differs depending on thequantity of component (A). Generally speaking, however, (C)/ (B) interms of molar ratio of 3-15 is preferred, inter alia, 4-10. The (C)/(A) ratio differs depending on the quantity of component (B), butnormally the preferred (C)/ (A) molar ratio ranges 0.5- 10. Forinstance, if the molar ratio of (C)/ (B) is 5, the preferred (C)/ (A)molar ratio is l-5.

The polymerization reaction can be performed by contacting the catalystwith isoprene in a hydrocarbon solvent under an inert gas atmosphere. Asfor the hydrocarbon solvent, aliphatic hydrocarbons such as pentane,hexane and heptane; cycloaliphatic hydrocarbons such as cyclopentane andcyclohexane; and aromatic hydrocarbons such as benzene and toluene, maybe used. As for the inert gas, nitrogen, argon, etc. may be used, butnitrogen is preferred for economical reasons. The polymerizationtemperature may vary over a considerable wide range, e.g., 0100 C., thepreferred range being 10"- 50 C. The polymerization pressure is notcritical, so far as it is sufficient to maintain the reaction mixture ina liquid phase. The suitable amount of the catalyst required is normallywithin the range of 0.0005-0.01 mol based on the amount of titanium perone mol of isoprene, the preferred range being approximately 0001-0005mol.

When the polymerization reaction has proceeded to the desired stage, thereaction can be terminated by the accepted practice. Then the productpolymer is separated, washed and dried by a conventional method toobtain the polyisoprene.

the product polymer shown no substantial change over a wide range ofAl/Ti molar ratio in the catalyst, e.g., from 1.5 to 3.0. This is indeedsurprising when the fact is considered that for the conventionaltitanium tetrachloridetrialkylaluminium catalyst system, the Al/Ti molarratio The high molecular weight polyisoprene obtained by 5 therein mustbe controlled within a very narrow range of, the present process willpossess a high cis-1,4 structure, say, O.8l.3 to exhibit a highactivity. having a cis content of normally no less than 96%, or EXAMPLES7 AND 8 under preferred polymerizatlon conditions 98% or more, asdetermined with infrared absorption spectrum analysis. 10 In theseexamples, the order of adding the catalyst and Hereinafter the inventionwill be explained with refermonomer was varied to determine itssignificance. In ence to the examples, which, however, are by no meansEXa P t Catalyst components were mixed in the intended to be limitative.In the examples, the boron tripresence of entire monomer to bepolymerized. Whereas fluoride-phenol complex employed was a red orreddish in Example 8, the components were mixed in advance to purple,slightly viscous liguid having a melting point of form the catalyst, andto which the monomer was added. 3.5 C., and contains 26.5i0.5% by weightof BF The Polymefllallon Was Performed in a glass Thi corresponds to BF-2C H OH Schlenk-type ampule. First 35 ml. of hexane was charged,

The intrinsic viscosity [1 of each polyisoprene was and in EXamPle 7,the Components Were added in the measured in toluene at 30 C, followingorder: isoprene, triethyl-aluminium, boron tri- The gel content of eachproduct was determined as folfluoride-Phenol Complex, and titaniumtetrachloride I11 low A 02% b weight ol ti f th d t i Example 8, theorder was as follows: triethylaluminium, toluene was filtered through aZOO-mesh stainless steel boron trilhloflde-phehol eoIhPleX, titaniumtetrachloride, screen, and the solid content remaining on the screen andisoprene The ampule Was melt'sealed and p in a wa ea ed, rotary reactionbath at 10 C. for 5 hours. The amounts The micro-structure of thepolymer was determined by of the Components p y Were as follows:isoprene, measuring the infrared absorption spectrum of thepolytrlethylalumihlum, mllllmols; boron mer solution in carbondisulfide, and calculating the filloTlde-PheholcomPleX, mllllmohalldtitanium tetrastructure from the measured result in accordance withchloride, mllllmol- The Post-treatments following the Richardsons th d[1, P l S i, 10 353 (1953) polymerization reaction were similar to thosein Examples EXAMPLES 1-6. The results are shown herembelow.

A glass Schlenk-type ampule of 100 ml. capacity was Yi 1d Gist-1,:charged with 30 ml. of n-hexane, 6.8 g. of isoprene, a tri- (percefm)[71] 223 31 ethylaluminium solution in n-hexane (concentration: 0.5mol/1.), a boron trifluoride-phenol complex solution in 35 35 M 98toluene (concentration: 0.2 mol/1.) and 1 ml. of titanium 8 52 5.2 98tetrachloride solution in hexane (concentration: 0.5 mol/1.). Thecomponents were introduced into the am- EXAMPLE 9 e order, e at roomtempereture (25." In this example, the polymerization reaction wasperwh1le vigorous stirring. The hexane solution of triethyl- 40 formedin a Similar manner as Examples except that a1um 1mum and the tolueneSolutlon the boron the proportions of the catalyst components wereselected fiuonde'phenol Complex were Charged e amounte as Al/B=4, andAl/Ti=2. The amounts of the catalyst that the B P who was constantlyWhlle the Al/ T1 components employed were as follows: titaniumtetramolar P Vaned from as mdleated m Table 1 chloride, 0.5 millimol;triethylaluminium, l millimol; and below. Finally the balance amount ofn-hexane was addboron trifiuoride pheno1 complex, 025 millimoL ed tomake the total amount of the mixture ml. The The yield f thepolyisoprene having an of was foregoing operations were all performedunder the atmos- 53% phere of nitrogen gas. The ampule was immediatelymelt- EXAMPLES 1041 sealed and kept in a rotary reaction bath for 5hours at 30 C. After completion of the reaction, the reaction 50 In asimilar manner as described in Examples a mixture was poured intomethanol which contained 2,6- yp ampule Was charged Wlth 35 IIllofdi-tert-butyl-phenol as an antioxidant, in order to inacnjheXaHe,millimols mol/lhexane Solution) of tivate the catalyst and precipitatethe polymer, The poly trlethylaluminium, II'lOl/l. toluene S0111- merwas vacuum dried at 40 C. for 24 hours. The results tloll) of boronlfllluoflde'phehol Complex, and milliare shown i T bl 1 55 mol (0.5mol/l. hexane solution) of titanium tetrachlo- TABLE 1 ride, at thetemperature indicated below. Thereafter the catalyst was aged for anhour at the same temperatures Yield under vigorous stirring. Then 6.8 g.of isoprene was added ratio) (percent) [1,] thereto, and the melt-sealedampule was kept at 10 C. Example Number: for 5 hours to permit thepolymerization reaction of the 1 1.0 55 3.9 content. The results were asfollows:

1.5 74 4.2 2.0 77 4.8 2. 5 72 4. 5 Tempera- 3. 0 66 4. 7 ture Yield 3. 560 3.9 (p 1] For comparison, a series of control experiments were 30 725.0 run in the similar manner to Examples 1-6, except that 40 52 the useof the boron trrfluonde-phenol complex was EXAMPLE 12 omitted. The Al/Ti molar ratios were also varied for each run. The best result wasobtained when Al/Ti=l, in which the yield was 63% and the productpolymer had an of 2.7.

From the foregoing results, it can be understood that when the catalystof this invention is used, the polymerizing activity of the catalyst andthe molecular weight of In this example, the polymerization reaction wasperformed in a similar manner described in Examples lO-ll, except that0.34 g. of isoprene Was present during the aging period of the catalystfor 1 hour at 10 C.

The yield of the polyisoprene was 84%, and the polymer had an [1;] of5.3.

The high polymerizing activity of the catalyst employed in this exampleis indeed surprising, since such minor amount of titanium (0.005 mol permol of isoprene) at such low polymerization temperature as C. for suchshort reaction period as 5 hours achieved the production of such highmolecular weight ([7 ]:5.3) polyisoprene at such high yield as 84%.

EXAMPLE 13 A glass autoclave of 3 1. capacity was charged with 1820 ml.of n-hexane, 346.4 g. of isoprene, 43.2 millimols of triethylaluminium(1 mol/l. hexane solution), 9.4 millimols of boron trifluoride-phenolcomplex (0.5 mol/l. toluene solution), and 24 millimols of titaniumtetrachloride (0.5 mol/l. hexane solution), in the order stated, whileagitating at 20 C. Then the mixture was reacted at 20 C. for 8 hours.Then a toluene-methanol mixed solvent (volume ratio=7:3) containing2,6-di-tertbutylphenol as an antioxidant was added to the reactionmixture to stop the polymerization reaction, and the reaction mixturewas poured into a large quantity of methanol to precipitate the polymer.The polymer was washed and dried at 40 C. for 24 hours at a reducedpressure. Thus obtained polyisoprene (yield=70%) contained 49% of gel,and had a Mooney viscosity, ML (100 C.), of 88.

EXAMPLE 14 A glass autoclave of 3 1. capacity was charged with 1840 ml.of n-hexane, 48 millimols (2 mols/l. hexane solution) oftriethylaluminium, 9.6 millimol (0.5 mol/l. toluene solution) of borontrifluoridephenol complex, and 24 millimols (0.5 mol/l. hexane solution)of titanium tetrachloride, in the order stated, while agitating at 30 C.The mixture was aged for an hour at 30 C. Then 346.4 g. of isoprene wasadded thereto, followed by 3 hours polymerization reaction at 10 C. andadditional 3 hours polymerization reaction at 15 C. The termination ofpolymerization reaction and the subsequent treatments were performedsimilarly as in Example 13.

The polyisoprene thus obtained at an yield of 84% had a Mooney viscosityML (100 C.) of 94 and a gel content of 3%.

EXAMPLE 15 A glass autoclave of 3 1. capacity was charged with 1820 ml.of n-hexane, 5.2 g. of isoprene, 60 millimols (2 mols/l. hexanesolution) of triethylaluminium, l2 millimols (0.5 mol/l. toluenesolution) of boron trifluoridephenol complex and 24 millimols (0.5mol/l. hexane solution) of titanium tetrachloride, in the order stated,at C. The catalyst was aged for an hour at this temperature withstirring. Then 346.4 g. of isoprene was added to the autoclave, andpolymerized at 10 C. for 5 hours. The termination of the polymerizationand the subsequent treatments were performed in the similar mannerdescribed in Example 13.

The polyisoprene thus obtained at an yield of 89% had 6 a Mooneyviscosity, ML C.), of 73 and [4;] of 4.2. Its gel content was 0.9%.

From the Examples 13 to 15 it can be understood that by varying thepreparation conditions of the catalyst, particularly the presence ofisoprene during the catalyst preparation and if present, the amount ofthe isoprene, and the aging condition of the catalyst, the gel-formingfunction of the catalyst can be varied over a wide range, howeverwithout affecting the desirable high polymerizing activity.

EXAMPLES 16-18 In these examples, isoprene was polymerized with the samemanner as in Example 1 except that boron trifluoride-meta-cresol complex(BF 1-65C- H OH) was used instead of BF -2C H OH and the Al/ B molarratio was varied as shown below.

Al/B, Al/Ti,

1. Process for the preparation of a high molecular weightcis-1,4-polyisoprene, which comprises contacting isoprene in ahydrocarbon solvent with a catalyst which is obtained by admixing (A) atitanium tetrahalide, (B) a complex of boron trifiuoride with a phenol,and (C) a trialkylaluminium.

2. Process for the preparation of a high molecular weightcis-1,4polyisoprene which comprises contacting isoprene in a hydrocarbonsolvent with a catalyst which is obtained by adding (A) a titaniumtetrahalide to a reaction mixture of (B a complex of 'boron) trifiuorideand a mononucleus monohydric phenol with (C) a trialkylaluminium, theproportions of the three catalyst components being such that the molarratio of Ti to Al is from 120.5 to 1:10, and the molar ratio of Al to Bis from 3:1 to 15:1.

3. The process of claim 2, in which the catalyst in prepared in thepresence of isoprene in-an amount of up to ten molar times that of thetitanium tetrahalide employed.

4. The process of claim 2, in which the mononucleus monohydric phenol isphenol.

References Cited UNITED STATES PATENTS 2,922,782 1/ 1960 Hay 26094.93,196,116 7/1965 Klopfer et al 252429 JOSEPH L. SCHOFER, PrimaryExaminer R. A. GAITHER, Assistant Examiner

